This is an article which discusses the increase in storage capacity while performance and hard error rates have not improved significantly in years, and what this means for protecting data in large storage systems. "The concept of parity-based RAID (levels 3, 5 and 6) is now pretty old in technological terms, and the technology's limitations will become pretty clear in the not-too-distant future â€" and are probably obvious to some users already. In my opinion, RAID-6 is a reliability Band Aid for RAID-5, and going from one parity drive to two is simply delaying the inevitable."

I also wonder what is the comparable time to rebuild a raidz volume to what the author presented here.

The time to rebuild a RAIDz array depends not on the array size, but on the used data size of the array. RAIDz only rebuilds the blocks referenced by the higher levels of the filesystem stack, which is possible because it is so integrated with the higher level fileystem.